Impellers or coupling hubs and the like used in compressors, pumps and related machinery are currently being mounted on associated shafting by utilizing hydraulic fluid under high pressure. This pressure is admitted into the impeller bore and acts to expand the bore to provide sufficient clearance to permit advancing the impeller hub onto the shaft during assembly. Once the impeller is in position, the hydraulic fluid pressure is reduced, thereby allowing the bore to contract so that the impeller hub grips the shaft with a precalculated interference fit.
In order to remove the impeller from the shaft, it has generally been necessary to heat it with a torch or the like to expand it enough to release the interference fit between the impeller and the shaft, or alternatively, use a suitable pulling device to pull the impeller off the shaft. While heating the impeller with a torch accommodates its removal from the shaft, this generally cannot be done where the pump or compressor is used in a chemical plant or the like where explosive vapors may be ignited by the open flame of the torch. In this type of situation, it has been the practice to use a mechanical pulling device to separate the impeller from the shaft. However, in many cases where there is a very high interference fit and a small angle of taper, the force required to pull the impeller off the shaft exceeds the capacity of the pulling devices which can be used at the location where the compressor or pump is installed. Consequently it has often been necessary to move the entire compressor or pump to an area where it is safe to use an open flame for the removal operation. In practice this has proven to be a relatively complicated and costly procedure.
The prior art also teaches the use of hydraulic fluid pressure to reduce the interference fit between an impeller hub and a shaft when the hub is to be removed from the shaft as well as when it is mounted on it. For example U.S. Pat. Nos. 2,840,399 and 3,061,342 teach the use of pressurized grease as the hydraulic medium so that lubrication of the shaft is obtained in conjunction with hub expansion. However, in these devices the interference fit at the interface of the hub and the shaft defines a highly tapered cone with a relatively low pressure interference fit between the hub and the shaft. In contrast to the foregoing patents, U.S. Pat. No. 2,946,610 shows a related arrangement utilizing hydraulic pressure in a relatively complicated hub and shaft structure having a stepped design wherein the interface between the hub and the shaft is divided into at least two step portions of progressively larger diameters. This accommodates installing the hub on the shaft in a relationship which provides a space between the internal radial face portions of the steps. Thus, when it is desired to separate the interference fit between the hub and the shaft, fluid is supplied under pressure into each of the spaces which acts to move one member axially relative to the other.